Stator-fixed structure and driving unit

ABSTRACT

A driving unit includes a stator, a housing including a tubular section to accommodate the stator, a cover coupled to the housing to block an upper opening of the tubular section, and a bent wire rod defined by a wire to press the stator against the tubular section, the bent wire rod being arranged between a top surface of the stator and a rear surface of the cover while being compressingly deformed along an axis of the stator. The bent wire rod has an annular or substantially annular shape with an opened portion when seen along the axis, and includes projections projecting upward along the axis and depressions projecting downward along the axis being arranged alternately and successively. An elastic force from the bent wire rod causes the stator to receive a downward force along the axis. The stator is pressed against the tubular section to hold the stator in the housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stator-fixed structure and a drivingunit. More particularly, the present invention is directed to techniquesof fixing a stator to a housing.

2. Description of the Related Art

Conventionally, a motor or a generator has been known including astator, a rotor in the interior of the stator, and a case accommodatingthe stator and the rotor. The stator is fixed to the case by bolts orscrews. See, for example, Japanese Patent Publication No. H06-70523A.Otherwise, the stator is adhered to the case via an adhesive. Such hasalso been known.

Examples of the conventional art with the construction described above,however, have the following drawbacks. That is, fixing the stator to thecase by bolts or the like takes much time for assembly since the boltsrequire fastening upon fixing the stator. Such an inconvenience mayoccur. Moreover, portions for fixing the stator by bolts or the like arerequired, and thus such portions may lead to another inconvenience of acomplex construction. On the other hand, fixing the station with anadhesive may lead to an inconvenience of increased time for assemblyincluding a cure time for the adhesive. Moreover, working efficiencyeasily decreases due to adhesion of the adhesive to a hand or the likeof an operator. Such an inconvenience may also occur.

SUMMARY OF THE INVENTION

In view of the state of the art described above, a preferred embodimentof the present invention provides a stator-fixed structure and a drivingunit with a simple construction that allows the stator to be fixed in ashort period of time.

A preferred embodiment of the present invention discloses a stator-fixedstructure. The stator-fixed structure includes a stator, a housingincluding a tubular section to accommodate the stator, a cover coupledto the housing to block an upper opening of the tubular section, and abent wire rod defined by a wire to press the stator against the tubularsection, the bent wire rod being arranged between a top surface of thestator and a rear surface of the cover while being compressinglydeformed along an axis of the stator. The bent wire rod has an annularor substantially annular shape with an opened portion when seen alongthe axis, and includes projections projecting upward along the axis anddepressions projecting downward along the axis arranged alternately andsuccessively, the projections contacting the rear surface of the coverand the depressions contacting the top surface of the stator.

The bent wire rod is defined by a wire, and has an annular orsubstantially annular shape with an opened portion when seen along theaxis. Examples of the substantially annular shape include a shapedefined by only curves such as a circle or an ellipse, a shape definedby straight lines such as a polygon, and a shape defined by straightlines and curves.

The bent wire rod includes alternate projections and depressionsarranged successively, the projections projecting upward along the axisand the depressions projecting downward along the axis. In a preferredembodiment of the present invention, it is assumed that a directionalong the axis of the stator from the stator toward the cover is anupward direction and a direction opposite thereto is a downwarddirection. Accordingly, when seen around the axis, the bent wire rodpreferably has a zigzag or a wavy shape with the alternate projectionsand depressions arranged successively along the axis. Connectionsbetween the projections and depressions may be linear or curved.

When such a bent wire rod is provided between the stator and the cover,the projections contact the rear surface of the cover and thedepressions contact the top surface of the stator. In addition, the bentwire rod is compressingly deformed along the axis. Accordingly, the bentwire rod generates an elastic force extending along the axis. Theelastic force causes the stator to undergo a downward force along theaxis. Then the stator is pressed against the tubular section so as to beheld in the housing. This suitably prevents or reduces shifting of thestator along the axis.

The elastic and deformable bent wire rod absorbs variations in thedimension of the stator or the cover along the axis, and thus suitablypresses the stator against the tubular section.

The stator-fixed structure described above does not use bolts or thelike to fix the stator thus achieving a simple construction. Inaddition, the stator is fixed to the housing by merely providing thebent wire rod between the stator and the cover resulting in an enhancedworking efficiency. The location of the stator is fixed in a shortperiod of time.

One of the directions along the axis is defined as an upward directionand the other direction as a downward direction. The direction along theaxis, however, is not limited to a specific direction, such as avertical direction. That is, the stator may be disposed in any directionand attitude, and accordingly the axis may extend in any direction.

In a preferred embodiment of the present invention, it is preferablethat the bent wire rod includes a plurality of corners and a pluralityof straight portions so as to define a substantially polygonal shapewhen seen along the axis, the straight portions connecting adjacentcorners to each other. The bent wire rod preferably has a polygonal orsubstantially polygonal outer shape when seen along the axis. The cornerwhere the wire rod is bent corresponds to a vertex of the polygonal orsubstantially polygonal shape. The straight portion where the wire rodextends linearly or substantially linearly corresponds to a side of thepolygonal or substantially polygonal shape. The bent wire rod withstraight portions is made with more ease than an outer shape with onlycurves.

In a preferred embodiment of the present invention, the corners arepreferably arranged at the projections or the depressions. For instance,when the corners are located at the same positions as the projections,the wire rod is bent at one of the projections in a direction wherebending following the projections and bending following the corners arecombined. When the corners are located at the same positions as thedepressions, the wire rod is bent at one of the depressions in adirection where bending following the depressions and bending followingthe corners are combined. Every corner is provided with a projection ora depression, and thus the corners serve as the projections or thedepressions. The number of bent portions of the wire rod is independentof the number of corners, and thus the total number of the bent portionsis defined by the total number of the projections and depressions.Consequently, making the bent wire rod is facilitated.

In a preferred embodiment of the present invention, the projections andthe depressions are preferably bent such that the bent wire rod has apolygonal or substantially polygonal outer shape with the projectionsand the depressions defining vertices when seen along the axis. Inaddition, the bent wire rod preferably includes straight portionsconnecting adjacent projections and depressions. The projections anddepressions are bent so as to project along the axis and to be a vertexof the polygonal or substantially polygonal shape when seen along theaxis. As a result, the bent wire rod has essentially a uniform shaperegardless of whether it is upside-down. For instance, a portionprojecting in one direction along the axis may serve as a projection ora depression. This reduces the work load of assembling the bent wirerod.

In a preferred embodiment of the present invention, it is preferablethat the bent wire rod is shaped to have a dimension larger than theexternal diameter of the stator when seen along the axis, and ispreferably assembled while being deformed so as to have a smaller outershape. The bent wire rod is partially open when seen along the axis.Consequently, the bent wire rod is deformable radially and inwardlyrelative to the axis so as to have a smaller outer shape. In addition,the bent wire rod has a polygonal or substantially polygonal shapelarger than the external diameter of the stator when seen along theaxis. Accordingly, when the bent wire rod is assembled while beingdeformed so as to have a smaller outer shape, the bent wire rod contactsa peripheral edge of the stator.

In a preferred embodiment of the present invention, the bent wire rod ispreferably defined by a wire rod having a circular cross-section. Thewire rod having the circular cross-section can be bent in any direction.Consequently, making the bent wire rod can be facilitated.

In a preferred embodiment of the present invention, the cover preferablyincludes a side wall and a protrusion. The side wall is provided on arear surface of the cover in a peripheral direction about the axis, andcontacts the bent wire rod to receive an elastic force radially andoutwardly relative to the axis that is generated by the bent wire rod.The protrusion projects from the side wall radially and inwardlyrelative to the axis to contact the projection and to receive an upwardelastic force along the axis that is generated by the bent wire rod.Accordingly, the radial and outward elastic force of the bent wire rodexpands the bent wire rod along the periphery of the side wall, and thusthe bent wire rod itself rests on the side wall. This facilitatesresting of the bent wire rod on the cover. In addition, the protrusionreceiving the upward elastic force along the axis projects from the sidewall, such that the bent wire rod is deformed compressingly whileresting on the side wall. Consequently, coupling of the cover to thehousing permits the bent wire rod to be compressingly deformed in agiven position in one operation. As described above, the stator is fixedto the housing with high efficiency.

In a preferred embodiment of the present invention, the side wallpreferably has an internal diameter slightly larger than an externaldiameter of the stator. This allows an upper portion of the stator to beaccommodated partially inside the side wall. As described above, partialaccommodation of the stator inside the cover facilitates a sizereduction.

In a preferred embodiment of the present invention, the protrusion ispreferably inclined downwardly along the axis and radially toward theaxis. A recess into which the projections are held is preferablyprovided between the protrusion and the side wall. The protrusionpressed by the bent wire rod upwardly along the axis is inclineddownwardly and radially toward the axis. Such a protrusion prevents orreduces shifting of the bent wire rod (projection) radially inward. Thatis, a contact position of the bent wire rod with the cover suitablyprevents or reduces radial shifting of the bent wire rod.

In a preferred embodiment of the present invention, the statorpreferably includes a stator core and coils formed by winding the statorcore with a winding. The bent wire rod preferably contacts a top surfaceof the stator core directly. The stator core preferably has a rigidityhigher than that of the coil. The bent wire rod directly contacts thestator core having a relatively higher rigidity to achieve accuratepressing of the stator.

In a preferred embodiment of the present invention, the statorpreferably further includes a restricting element disposed on the topsurface of the stator core and inside from an outer peripheral edge ofthe stator core to restrict shifting of the bent wire rod radiallyinward. The restricting element suitably prevents or reduces radialshifting of the contact position of the bent wire rod with the stator.In other words, shifting of the depressions of the bent wire rod issuitably prevented or reduced.

In a preferred embodiment of the present invention, the statorpreferably includes an insulated bobbin disposed between the stator coreand the coils to cover the stator core. The restricting element ispreferably integrated with the insulated bobbin. The insulated bobbinserves as the restricting element resulting in a simplified structure.

Another preferred embodiment of the present invention includes a drivingunit. The driving unit includes a motor configured to generate power,the motor including a rotor and a stator outside of the rotor, a housingincluding a tubular section accommodating the motor, a cover coupled tothe housing to block an upper opening of the tubular section, and a bentwire rod defined by a wire rod, the bent wire rod being disposed betweena top surface of the stator and a rear surface of the cover while beingcompressingly deformed along an axis of the stator to press the statoragainst the tubular section. The bent wire rod is annular orsubstantially annular and includes an opened portion when seen along theaxis, and includes projections projecting upward along the axis anddepressions projecting downward along the axis arranged alternately andsuccessively, the projections contacting the rear surface of the coverand the depressions contacting the top surface of the stator.

The driving unit according to a preferred embodiment of the presentinvention including the stator-fixed structure described above.Consequently, variations in the dimensions of the stator or the coveralong the axis are absorbed to suitably prevent or reduce shifting ofthe stator along the axis. In addition, the construction of the drivingunit is compact. Moreover, the stator is fixed to the housing by merelyarranging the bent wire rod between the stator and the cover, resultingin an enhanced working efficiency and assembly in a short period oftime. Accordingly, efficient assembly of the driving unit can beachieved.

In a preferred embodiment of the present invention, the driving unit ismountable on a bicycle. The housing further includes a crankshaftchamber into which a crankshaft of the bicycle is inserted. The motorgenerates power to assist pressure on the pedals coupled to thecrankshaft. Such a construction is preferable. The pedals of the bicycleoften first contact the ground. The crankshaft is coupled the pedals.Accordingly, in the driving unit mounted on the bicycle, a shock may beapplied directly to the housing, and in addition, a shock may be applieddirectly inside the driving unit (crankshaft chamber) via thecrankshaft. In the latter, a strong force is applied to the stator alongthe axis. On the other hand, the driving unit according to a preferredembodiment of the present invention includes the stator-fixed structuredescribed above, and thus shifting or disconnection of the stator alongthe axis is suitably prevented or reduced. Consequently, the drivingunit according to a preferred embodiment of the present invention issuitably applicable to bicycles, for example.

In the stator-fixed structure according to a preferred embodiment of thepresent invention, the projections of the bent wire rod contact the rearsurface of the cover, and the depressions of the bent wire rod contactthe top surface of the stator. Moreover, the bent wire rod iscompressingly deformed along the axis. This causes the bent wire rod togenerate an elastic force extending along the axis. The elastic forceexerts an upward force along the axis to the cover and a downward forcealong the axis to the stator. Then the stator is pressed against thetubular section to be held in the housing. Consequently, shifting of thestator along the axis is suitably prevented or reduced.

In addition, the elastically deformable bent wire rod absorbs variationsin the dimensions of the stator or the cover along the axis thusachieving suitable pressing of the stator against the tubular section.

The stator-fixed structure described above does not use bolts or thelike to fix the location of the stator, thus achieving a simpleconstruction. In addition, the stator is fixed to the housing by merelyarranging the bent wire rod between the stator and the cover resultingin enhanced working efficiency. The location of the stator is fixed in ashort period of time.

The driving unit according to a preferred embodiment of the presentinvention includes the stator-fixed structure. Consequently, variationsin the dimensions of the stator or the cover along the axis are absorbedsuitably preventing or reducing shifting of the stator along the axis ofthe stator. Moreover, this achieves a simple construction of the drivingunit. Furthermore, the stator is fixed to the housing by merelyproviding the bent wire rod between the stator and the cover resultingin an enhanced working efficiency and assembly in a short period oftime. Accordingly, efficient assembly of the driving unit can beachieved.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of a driving unit according to a preferredembodiment of the present invention.

FIG. 2 is a plan view of a principal portion of the driving unit.

FIG. 3 is a sectional view along arrow III-III in FIG. 1.

FIG. 4 is a perspective view of a principal portion of a housing.

FIG. 5 is a perspective view of a principal portion of a stator.

FIGS. 6 and 7 are enlarged sectional views each illustrating astator-fixed structure.

FIG. 8 is an exploded perspective view of a principal portion of thedriving unit.

FIG. 9 is an external perspective view of a spring pin.

FIG. 10 is a perspective view of a rear surface of a cover.

FIG. 11 is a perspective view of a bent wire rod.

FIG. 12A is a view of the bent wire rod illustrating a partial side viewof the bent wire rod as seen from a direction orthogonal to the axis ofthe stator, and FIG. 12B is a view of the bent wire rod illustrating aplan view of the bent wire rod as seen along the axis of the stator.

FIG. 13 is a left side view of a bicycle including the driving unitmounted thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description will be given hereinafter of preferred embodiments of thepresent invention with reference to drawings. A driving unit mountableon a bicycle will be described as one example of a preferred embodimentof the present invention. FIG. 1 is an external view of a driving unitaccording to a preferred embodiment of the present invention.

A driving unit 1 includes a housing 3 and a cover 5. The cover 5 isfastened to the housing 3 via bolts 7. A crankshaft 71 of a bicyclepasses through the driving unit 1.

FIG. 2 is a plan view of a principal portion of the driving unit 1. InFIG. 2, besides the cover 5 and the crankshaft 71 described above, arotor or the like is not shown. As illustrated, the housing 3 includes atubular section 11 that is cylindrical or substantially cylindrical. Thetubular section 11 accommodates a stator 13. A spring pin 15 is pressedinto a gap between the tubular section 11 and the stator 13.

FIG. 3 is a sectional view along arrow of III-III in FIG. 1. Asillustrated, a rotor 16 is disposed inside of the stator 13. The rotor16 is connected to a rotary shaft 17 so as to rotate integrally with therotary shaft 17. The rotary shaft 17 is rotatably supported in thehousing 3. The stator 13, the rotor 16, and the rotary shaft 17 define amotor 18 that generates power. The rotary shaft 17 is interlocked withan output shaft 20 via a gear unit 19 or the like. The output shaft 20outputs power generated by the motor 18.

The cover 5 described above closes an upper opening of the tubularsection 11. The cover 5 contacts an upper end surface 27 of the tubularsection 11. A bent wire rod 51 is arranged between the cover 5 and thestator 13 while being compressingly deformed.

The housing 3 includes a left case 3L and a right case 3R in which theleft and right cases are separable from each other. Description is madebelow simply of the housing 3 unless there is a difference between theleft case 3L and the right case 3R.

In a preferred embodiment of the present invention, the term “axis R” isused throughout the specification assuming that the axis R of the stator13 substantially conforms to the central axis of the tubular section 11for convenience. In addition, in a preferred embodiment of the presentinvention, a direction along the axis of the stator 13 from the stator13 toward the cover 5 is referred to as an “upward direction along theaxis R” or “upward” for convenience. In addition, a direction oppositeto the direction from the stator 13 toward the cover 5 is referred to asa “downward direction along the axis R” or “downward”. For instance, anupper side of the plane of FIG. 3 is referred to as an “upside directionalong the axis R” or simply as the “upside”, whereas a lower side of theplane of the drawing is a “downside direction along the axis R” orsimply the “downside”, provided that this is not a limitation of adirection of the axis R to a specific direction such as a verticaldirection. That is, the stator 13 may be disposed in any direction andattitude and, accordingly, the axis R may extend in any direction. Adirection around the axis R is referred to as a “peripheral directionQ”.

FIG. 4 is a perspective view of a principal portion of the housing 3. InFIG. 4, only the left case 3L is illustrated and the right case 3R isomitted.

As illustrated, the tubular section 11 includes an inner wall 21 on theinside thereof. The inner wall 21 has an internal diameter slightlylarger than an external diameter of the stator 13, thus allowingaccommodation of the stator 13. The inner wall 21 includes a singlefirst groove 23 therein. In FIG. 4, the first groove 23 is disposed in aposition slightly different from that in FIG. 2.

On lower ends of the inner wall 21 and the first groove 23, a flange 24is provided that projects inwardly and radially relative to the axis R(hereinafter abbreviated as “radially” where appropriate). The flange 24has an internal diameter smaller than an external diameter of the stator13. The flange 24 contacts the stator 13 at a top surface thereof tosupport the stator 13.

The tubular section 11 further includes a plurality of (e.g., three)bosses 25 for connecting the cover 5 to the housing 3. The housing 3further includes a plate section 29 projecting externally from the outerwall of the tubular section 11. The plate section 29 serves as a walldefining a crankshaft chamber 72 into which the crankshaft 71 isinserted.

As illustrated in FIG. 3, the stator 13 includes a stator core 31, aninsulated bobbin 35, and a coil 37. The insulated bobbin 35 covers thestator core 31. The coil 37 includes a winding wound around the statorcore 31 over the insulated bobbin 35.

FIG. 5 is a perspective view of a principal portion of the stator. Asillustrated, a second groove 33 is provided on an outer wall 32 of thestator core 31, the second groove 33 being parallel or substantiallyparallel to the axis R. The second groove 33 has a semicircular orsubstantially semicircular shape. The stator core 31 further includes aplurality of teeth 34. A slot F is arranged between adjacent teeth 34.The second groove 33 is disposed radially outside of the slot F.

FIGS. 6 and 7 are each enlarged sectional views of the stator-fixedstructure. As illustrated, the insulated bobbin 35 includes a collar 36extending radially and outwardly to cover the top surface of the statorcore 31. The collar 36 has a diameter slightly smaller than the externaldiameter of the stator core 31. Accordingly, a peripheral edge 38 a ofthe top surface 38 of the stator core 31 is exposed.

FIG. 8 is an exploded perspective view of a principal portion of thedriving unit 1. As illustrated, the stator 13 is attached to the tubularsection 11 such that the second groove 33 opposes the first groove 23.This creates a circular or substantially circular gap defined by thefirst groove 23 and the second groove 33.

FIG. 9 is an external perspective view of the spring pin 15. Asillustrated, the spring pin 15 has a cylindrical or substantiallycylindrical shape, and includes a slit D parallel or substantiallyparallel to a shaft axis S. An upper end 15 a and a lower end 15 b ofthe spring pin 15 are preferably chamfered. The ends are each preferablytapered. When the spring pin 15 is compressingly deformed radially andinwardly toward the shaft axis S, the spring pin 15 exerts a elasticforce radially and outwardly relative to the shaft axis S.

As illustrated in FIG. 7, the spring pin 15 is pressed into the gapdefined by the first groove 23 and the second groove 33.

As illustrated in FIG. 2, when the spring pin 15 is pressed into the gapit is kept compressingly deformed, thus exerting an elastic force. Theelastic force causes the spring pin 15 to press against a portion of thestator 13 (stator core 31) thus pressing the opposite portion of thestator 13 against the inner wall 21 of the tubular section 11.Specifically, assuming that a direction from the shaft axis S of thespring pin 15 toward the axis R is a radial direction V and anintersecting point of the radial direction V and the inner wall 21 is apoint C, the stator 13 comes into surface contact with the inner wall 21within an area extending around the point C in the peripheral directionQ of the axis R.

The inner wall 21 in surface contact with the stator 13 undergoes a loadradially and outwardly relative to the axis R. This causes a frictionforce between the stator 13 and the inner wall 21. The friction forceholds the stator 13. That is, shifting of the stator 13 along the axis Ris suitably prevented or reduced.

Reference is made to FIGS. 6, 7, and 10. FIG. 10 is a perspective viewof the rear surface of the cover 5. The rear surface of the cover 5includes a side wall 41 therein. The side wall 41 is located along theperipheral direction Q of the axis R. The side wall 41 has an internaldiameter slightly larger than the external diameter of the stator 13.The stator 13 (stator core 31) projecting from the tubular section 11 isaccommodated inside the side wall 41. As described above, the upper sideof the stator 13 is partially accommodated in the cover 5 facilitating areduction in the size of the driving unit 1.

The side wall 41 includes a notch 43 therein. The notch is disposedalong an extended position of the first groove 23. As illustrated inFIG. 7, the spring pin 15 is accommodated in the notch 43, the springpin 15 projecting upward from the upper end surface 27 of the tubularsection 11. The spring pin 15 preferably has a length smaller than thedimension of the stator 13 along the axis R. Consequently, the springpin 15 does not project upward over the stator 13 (stator core 31).

The cover 5 also includes a protrusion 45. The protrusion 45 projectsradially and inwardly from an upper end of the side wall 41. Theprotrusion 45 is inclined downwardly along the axis R and radiallytoward the axis R. As a result, an annular recess (space) H is providedbetween the side wall 41 and the protrusion 45.

FIG. 11 is a perspective view of the bent wire rod 51. FIG. 12A is apartial side view of the bent wire rod 51 seen from a directionorthogonal to the axis R, and FIG. 12B is a plan view of the bent wirerod 51 seen along the axis R. FIG. 11 illustrates a bent wire rod 51 notcompressingly deformed, whereas FIG. 12 illustrates a bent wire rod 51compressingly deformed between the cover 5 and the stator 13.

The bent wire rod 51 is preferably defined by a single wire rod. Thewire rod preferably has a circular or substantially circularcross-section. The wire rod is preferably made of a metal such asstainless steel. Examples of the wire rod include round steel, aroundwire rod, a steel wire, and a round bar. The bent wire rod 51 is shapedby bending the wire rod as described above. Consequently, the bent wirerod 51 is composed of a portion of bending the wire rod and/or a portionof extending the wire rod linearly.

Reference is made to FIG. 12A. The bent wire rod 51 includes projections53 a and depressions 53 b arranged alternately and successively, theprojections 53 a being bent to project upward along the axis R and thedepressions 53 b being bent to project downward along the axis R.Consequently, when seen in the peripheral direction Q around the axis R,the bent wire rod 51 preferably has a zigzag or a wavy shape. Theprojections 53 a and depressions 53 b are preferably arranged at regularor substantially regular intervals.

Reference is made to FIG. 12B. The projections 53 a and the depressions53 b are also bent such that the bent wire rod 51 has a polygonal orsubstantially polygonal outer shape with the projections 53 a and thedepressions 53 b defining vertices when seen along the axis R. FIGS. 11and 12B clearly illustrate the projections 53 a surrounded by dashedline circles and the depressions 53 b surrounded by dashed linetriangles. As a result, the projections 53 a and the depressions 53 baccording to a preferred embodiment of the present invention alsocorrespond to corners of the bent wire rod 51.

A straight portion 55 is arranged between an adjacent projection 53 aand depression 53 b. The bent wire rod 51 includes ends 57 a and 57 b.Accordingly, the bent wire rod 51 has a polygonal or substantiallypolygonal shape including a portion partially opened when seen along theaxis R. FIG. 12B illustrates the bent wire rod 51 shaped to beequilateral icositetragon when seen along the axis R. With the openportion, the total number of the projections 53 a and the depressions 53b defining vertices is preferably twenty-three, for example.

The bent wire rod 51 having the above shape is compressingly deformablealong the axis R. When compressingly deformed along the axis R, the bentwire rod 51 extends along the axis R to exert an elastic force to causethe bent wire rod 51 to return to its original shape.

As described above, the bent wire rod 51 has a polygonal orsubstantially polygonal outer shape with only the projections 53 a anddepressions 53 b defining vertices, and no portion other than theprojections 53 a and depressions 53 b defining a vertex. Consequently,the bent wire rod 51 has essentially a uniform shape regardless ofwhether it is upside-down. Accordingly, a portion projecting in onedirection along the axis R may serve as a projection 53 a or adepression 53 b. This reduces the work load of assembling the bent wirerod 51.

The bent wire rod 51 has an opened portion at the ends 57 a and 57 b,and thus is compressingly deformable inwardly and radially relative tothe axis R so as to have a smaller outer shape. When compressinglydeformed radially and inwardly, the bent wire rod 51 generates anelastic force causing the bent wire rod 51 to expand radially andoutwardly to cause the bent wire rod 51 to return to its original shape.

The bent wire rod 51 is made in advance to have a polygonal shape havinga larger dimension than the external diameter of the stator 13 when seenalong the axis R. This allows the bent wire rod 51 to contact theperipheral edge 38 a of the stator 13. In a preferred embodiment of thepresent invention, the bent wire rod 51 is made in advance to have apolygonal shape having a dimension larger than the internal diameter ofthe side wall 41.

The stator 13 is fixed by the bent wire rod 51 as described below.Specifically, as illustrated in FIG. 10, the bent wire rod 51 isdisposed along the side wall 41 of the cover 5 while being compressed tohave a smaller outer shape. This causes the bent wire rod 51 to generatea radially outward elastic force by which the bent wire rod 51 expandsacross the entire periphery of the side wall 41. Then the bent wire rod51 itself rests on the side wall 41 so as not to disconnect from thecover 5 under its own weight.

The cover 5 on which the bent wire rod 51 rests is fastened to thehousing 3. Consequently, as illustrated in FIGS. 6 and 7, the bent wirerod 51 (depressions 53 b) contacts the peripheral edge 38 a of thestator core 31. The bent wire rod 51 (projections 53 a) contacts theprotrusion 45 along the side wall 41. Then the bent wire rod 51 iscompressingly deformable along the axis R. The compressingly deformedbent wire rod 51 exerts an elastic force along the axis R. Theprotrusion 45 receives an elastic force upward along the axis Rgenerated by the bent wire rod 51. The stator 13 receives an elasticforce downward along the axis R generated by the bent wire rod 51. Morespecifically, the stator core 31 receives an elastic force distributedby all of the depressions 53 b. As a result, the lower surface of thestator core 31 is pressed against the flange 24 of the tubular section11 thus preventing or reducing the shifting of the stator 13 along theaxis R.

As described above, the stator 13 is fixed by merely attaching the bentwire rod 51 to the cover 5 and coupling the cover 5 to the housing 3.Coupling the cover 5 to the housing 3 allows the bent wire rod 51 to becompressingly deformed in one operation in a given position to fix thestator 13 to the housing 3. This fixes the location of the stator 13 ina short period of time with high efficiency.

Moreover, the bent wire rod 51 is elasticity deformable. Consequently,variations in the dimension of the stator 13 or the cover 5 along theaxis R are compensated for so as to suitably press the stator 13 againstthe tubular section 11.

With the combination of fixing the location of the stator 13 by thespring pin 15 described above and fixing the location of the stator 13by the bent wire rod 51, the driving unit 1 according to a preferredembodiment of the present invention ensures prevention or significantreduction of the shifting of the stator 13 along the axis R.

Both the ends 57 a and 57 b of the bent wire rod 51 are designed not toproject beyond the projections 53 a and depressions 53 b along the axisR when the bent wire rod 51 is compressingly deformed along the axis Ras described above. Specifically, as illustrated in FIG. 12A, assumingthat an area between the projections 53 a and the depressions 53 b alongthe axis R is an area G, the ends 57 a and 57 b are always locatedwithin the area G. For instance, it is preferable that a distance fromthe end 57 a to the projection 53 a or the depression 53 b nearest tothe end 57 a is shorter than the length of a straight portion 55 betweenan adjacent projection 53 a and depression 53 b. It is more preferablethat this distance is about one third the length of the straight portion55, for example.

The bent wire rod 51 prevents the ends 57 a and 57 b thereof fromcontacting the top surface 38 of the stator core 31 and the protrusion45 of the cover 5. Consequently, this prevents or reduces variations inthe elastic force of the bent wire rod 51 along the axis R.

In addition, the ends 57 a and 57 b of the bent wire rod 51 do notcontact each other when the bent wire rod 51 is compressingly deformedradially as described above. Consequently, the elastic force of the bentwire rod 51 can be prevented from varying along the axis R and/orradially. If the ends 57 a and 57 b contact each other, a property ofthe bent wire rod 51 as an elastic body (a relationship between load andan elastic force) varies.

Moreover, the protrusion 45 is inclined downwardly along the axis Rradially and inwardly. Consequently, the bent wire rod 51 is not able tomove radially and inwardly unless the bent wire rod 51 itself is furthercontracted. The protrusion 45 suitably prevents or reduces radialshifting of the contact position of the bent wire rod 51 and the cover5. In other words, radial and inward shifting of the projections 53 a ofthe bent wire rod 51 is suitably prevented or reduced.

Moreover, the collar 36 of the insulated bobbin 35 has a dimensionslightly smaller than the external diameter of the stator core 31, andthus the top surface 38 of the stator core 31 (peripheral edge 38 a) isexposed. This causes the bent wire rod 51 to directly contact the topsurface 38 of the stator core 31, which has a relatively high rigidity.Consequently, the bent wire rod 51 allows the elastic force to act onthe stator 13 directly allowing the stator 13 to stably receive theelastic force.

As clearly illustrated in FIG. 6, the collar 36 extends adjacent to theouter peripheral edge 39 of the stator core 31. Accordingly, the collar36 suitably prevents or reduces radial shifting of the contact positionof the bent wire rod 51 to the stator 13. In other words, the collar 36suitably prevents or reduces shifting of the depressions 53 b of thebent wire rod 51. In addition, the collar 36 is integrated with theinsulated bobbin 35 simplifying the structure.

Moreover, the bent wire rod 51 is defined by a wire rod, and is thussuitably disposed within a narrow and annular area, such as theperipheral edge 38 a of the stator 13. Accordingly, a reduction in thesize of the stator 13 and the cover 5 is achieved. In addition, the bentwire rod 51 is formed preferably by bending the wire rod, and thus doesnot require a mold such as press dies resulting in low production costs.

The bent wire rod 51 preferably has an outer shape of a polygonincluding many vertices as seen along the axis R. Accordingly, the bentwire rod 51 suitably extends along the circumferential surface of theside wall 41. Moreover, many depressions 53 b of the bent wire rod 51lead to a decreased pressing by a single depression 53 b against thestator 13. In addition, the elastic force is distributed along thestator 13.

The spring pin 15 does not project above the stator 13, thus preventinginterference between the spring pin 15 and the bent wire rod 51.

The side wall 41 has an internal diameter slightly larger than theexternal diameter of the stator 13, and thus the stator 13 (stator core31) projecting from the tubular section 11 is accommodated inside theside wall 41. As described above, the upper portion of the stator 13 ispartially accommodated inside the cover 5 facilitating a reduction inthe size of the driving unit 1.

Description will be given next of an exemplary application of thedriving unit 1 to a bicycle, for example, according to a preferredembodiment of the present invention. FIG. 13 is a left side view of abicycle 61 with the driving unit 1 mounted thereon. The bicycle 61includes a body frame 63, a front wheel 65 and a rear wheel 67 rotatablysupported on the body frame 63, and a handle 69 supported on the bodyframe 63 to steer the front wheel 65.

The driving unit 1 is preferably supported on the body frame 63 aroundthe lower middle portion of the bicycle 61. The driving unit 1 isprovided such that the axis R is horizontal or substantially horizontal.The driving unit 1 includes a crankshaft 71 passing therethroughsubstantially horizontally. The crankshaft 71 includes pedals 73 coupledthereto on both ends thereof. Pressure on the pedals 73 causes thecrankshaft 71 to rotate. Rotary power of the crankshaft 71 istransmitted to the rear wheel 67 via a chain 75. In addition, the bodyframe 63 includes a battery 77 supported thereon. The battery 77 drivesthe motor 18 defined by the stator 13 and the like.

Reference is now made to FIG. 3. The crankshaft 71 is inserted into thecrankshaft chamber 72 of the driving unit 1. The crankshaft chamber 72also includes a torque sensor (not shown) that detects torque of thecrankshaft 71, and a controller (not shown) that controls the motor 18.Power from the motor 18 is output to an output shaft 20. Rotary powerfrom the output shaft 20 is transmitted to the rear wheel 67 via thechain 75.

The controller controls the motor 18 in accordance with detectionresults from the torque sensor. The motor 18 generates auxiliary powerin accordance with the pressure on the pedals 73. The pressure on thepedals 73 and the power from the motor 18 are transmitted to the chain75 via the crankshaft 71 and the output shaft 20, respectively. Thechain 75 combines the pressure on the pedals 73 and the power from themotor 18 to transmit the combined pressure and power to the rear wheel67. This causes the bicycle 61 to move.

In the bicycle 61, the pedals 73 often contact the ground first. Thepedals 73 are coupled to the crankshaft 71. Accordingly, the surface ofthe driving unit (the outer surface of the housing) of the bicycle 61may undergo shock directly, or the interior of the driving unit (crankchamber) may undergo shock directly through the crankshaft. When shockis directly transmitted inside of the driving unit, a strong force istransmitted to the stator along the axis R. On the other hand, in thedriving unit 1 according to a preferred embodiment of the presentinvention, the fixed structure of the stator 13 described above is used.This suitably prevents or reduces shifting of the stator 13 along theaxis R. Consequently, the driving unit 1 according to a preferredembodiment of the present invention is suitable for mounting on thebicycle 61.

The present invention is not limited to the above preferred embodiments,but may be modified as described below.

The preferred embodiments described above both fix the stator 13 by thebent wire rod 51 and by the spring pin 15. However, this is notlimitative. Specifically, the spring pin 15 may be omitted.

In the preferred embodiments described above, the shape of the bent wirerod 51 seen along the axis R preferably is an equilateral icositetragonas one example, but the present invention is not limited to this. Thatis, the number of vertices of the polygon may be selected and varied asappropriate. For instance, the polygon may be duodecagonal or more. Inaddition, the shape is not limited to be an equilateral polygon, but maybe a polygon other than this. Alternatively, the shape may be modifiedinto a circle, an ellipse or the like.

In the preferred embodiments described above, the bent wire rod 51 has apolygonal or substantially polygonal shape seen along the axis R withthe projections 53 a and the depressions 53 b only defining thevertices. However, this is not limitative. For instance, assuming that aportion corresponding to the vertex of the polygon is a corner, thecorner may be provided besides the projections 53 a and the depressions53 b independently of the projections 53 a and the depressions 53. Inother words, the corners may be disposed in a position different frompositions of the projections 53 a and the depressions 53 b.Alternatively, a projection 53 a and a depression 53 may partially serveas the corner. In this case, a corner may also be provided besides theprojections 53 a and the depressions 53.

In addition, one of the projections 53 a and depressions 53 b may serveas a corner, and the other does not serve as a corner. Such amodification may be used. For instance, each of the corners is providedtogether with the projection 53 a and not with the depression 53 b. Inthis case, when the bent wire rod 51 is seen along the axis R, thedepression 53 b is disposed between the adjacent vertices (corners) ofthe polygon (i.e., around the center of each side of the polygon).

In the preferred embodiments described above, the bent wire rod 51generates an elastic force radially and outwardly. However, this is notlimitative. Specifically, the bent wire rod may be modified asappropriate that generates no elastic force radially and outwardly.

In the preferred embodiments described above, the bent wire rod 51 isdefined by a wire rod having a circular cross-section, but is notlimited to this. For instance, the bent wire rod may be modified to bedefined by a wire rod having a rectangular or substantially rectangularcross-section.

In the preferred embodiments described above, the bent wire rod 51 restson the cover 5 (side wall 41), but is not limited to this. For instance,the bent wire rod 51 may be modified to rest on the tubular section 11.Alternatively, the bent wire rod 51 may rest on the stator 13.

In the preferred embodiments described above, the contact position ofthe bent wire rod 51 and the stator 13 is at the peripheral edge 38 a ofthe stator core 31. However, this is not limitative. The contactposition may be modified to be another position of the stator core 31.In addition, the bent wire rod 51 may be modified to contact an elementof the stator 13 other than the stator core 31 (e.g., the insulatedbobbin 35 or the coil 37).

In the preferred embodiments described above, the protrusion 45preferably is inclined, but is not limited to this. Specifically, theprotrusion 45 may project in a horizontal direction radially andinwardly relative to the axis R.

In the preferred embodiments described above, the collar 36 restrictingradial and inward shifting of the bent wire rod 51 is integrated withthe insulated bobbin 35. However, this is not limitative. Specifically,a restricting element restricting radial and inward shifting of the bentwire rod 51 may be provided besides the insulated bobbin 35.

The preferred embodiments described above suggest that the driving unit1 may be mounted to a bicycle, but the present invention is not limitedto this. Alternatively, the driving unit 1 may be mounted to any vehicleor device. Accordingly, the crankshaft chamber 72 may be omitted withthe modification above.

In the preferred embodiments described above, the stator 13 has beendescribed as one example of an element of the motor 18, but the presentinvention is not limited to this. For instance, preferred embodiments ofthe present invention may be applicable to the stator 13 defining agenerator.

The preferred embodiments and modifications described above may bemodified as appropriate. For instance, each construction may be modifiedas appropriate by replacing or combining it with other modifications.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

The invention claimed is:
 1. A stator-fixed structure comprising: astator; a housing including a tubular section to accommodate the stator;a cover coupled to the housing to block an upper opening of the tubularsection; and a bent wire rod defined by a wire to press the statoragainst the tubular section, the bent wire rod being arranged between atop surface of the stator and a rear surface of the cover while beingcompressingly deformed along an axis of the stator; wherein the bentwire rod has a substantially annular shape with an opened portion whenseen along the axis, and includes projections projecting upward alongthe axis and depressions projecting downward along the axis arrangedalternately and successively, the projections contacting the rearsurface of the cover and the depressions contacting the top surface ofthe stator; the stator includes a stator core and coils formed bywinding the stator core with a winding, and the bent wire rod directlycontacts a top surface of the stator core; and the stator includes arestricting element disposed on the top surface of the stator core andlocated inward relative to an outer peripheral edge of the stator coreto restrict shifting of the bent wire rod radially inward.
 2. Thestator-fixed structure according to claim 1, wherein the stator includesan insulated bobbin disposed between the stator core and the coils tocover the stator core, and the restricting element is integral with theinsulated bobbin.
 3. A driving unit comprising: a motor that generatespower and includes a rotor and a stator outside of the rotor; a housingincluding a tubular section accommodating the motor; a cover coupled tothe housing to block an upper opening of the tubular section; and a bentwire rod defined by a wire, the bent wire rod being disposed between atop surface of the stator and a rear surface of the cover while beingcompressingly deformed along an axis of the stator to press the statoragainst the tubular section; wherein the bent wire rod is substantiallyannular and includes an opened portion when seen along the axis, andprojections projecting upward along the axis and depressions projectingdownward along the axis arranged alternately and successively; theprojections contact the rear surface of the cover and the depressionscontact the top surface of the stator; the stator includes a stator coreand coils formed by winding the stator core with a winding, and the bentwire rod directly contacts a top surface of the stator core; and thestator includes a restricting element disposed on the top surface of thestator core and located inward relative to an outer peripheral edge ofthe stator core to restrict shifting of the bent wire rod radiallyinward.
 4. The driving unit according to claim 3, wherein the drivingunit is mounted on a bicycle, the housing includes a crankshaft chamberinto which a crankshaft of the bicycle is inserted; and the motorgenerates power to assist pressure on pedals coupled to the crankshaft.